Short-time rotational diffusion in monodisperse charge-stabilized colloidal suspensions

We investigate the combined effects of electrostatic interactions and hydrodynamic interactions on the short-time rotational self-diffusion coefficient in charge-stabilized suspensions. We calculate this coefficient as a function of volume fraction for various effective particle charges and amounts of added electrolyte. The influence of the hydrodynamic interactions on the rotational diffusion coefficient is less pronounced for charged particles than for uncharged ones. Salt-free suspensions are weakly influenced by hydrodynamic interactions. For these strongly correlated systems we obtain a quadratic volume fraction-dependence of the diffusion coefficient, which is well explained in terms of an effective hard sphere model.Comment: 21 pages, LaTeX, 7 Postscript figures included using epsf, to appear in Physica

Dynamics of coupled spins in the white- and quantum-noise regime

We study the dynamics of dissipative spins for general spin-spin coupling. We investigate the population dynamics and relaxation of the purity in the white noise regime, in which exact results are available. Inter alia, we find distinct reduction of decoherence and slowdown of purity decay around degeneracy points. We also determine in analytic form the one-phonon exchange contribution to decoherence and relaxation in the ohmic quantum noise regime valid down to zero temperature.Comment: 8 pages, 5 figure

Submodular Minimization Under Congruency Constraints

Submodular function minimization (SFM) is a fundamental and efficiently solvable problem class in combinatorial optimization with a multitude of applications in various fields. Surprisingly, there is only very little known about constraint types under which SFM remains efficiently solvable. The arguably most relevant non-trivial constraint class for which polynomial SFM algorithms are known are parity constraints, i.e., optimizing only over sets of odd (or even) cardinality. Parity constraints capture classical combinatorial optimization problems like the odd-cut problem, and they are a key tool in a recent technique to efficiently solve integer programs with a constraint matrix whose subdeterminants are bounded by two in absolute value. We show that efficient SFM is possible even for a significantly larger class than parity constraints, by introducing a new approach that combines techniques from Combinatorial Optimization, Combinatorics, and Number Theory. In particular, we can show that efficient SFM is possible over all sets (of any given lattice) of cardinality r mod m, as long as m is a constant prime power. This covers generalizations of the odd-cut problem with open complexity status, and with relevance in the context of integer programming with higher subdeterminants. To obtain our results, we establish a connection between the correctness of a natural algorithm, and the inexistence of set systems with specific combinatorial properties. We introduce a general technique to disprove the existence of such set systems, which allows for obtaining extensions of our results beyond the above-mentioned setting. These extensions settle two open questions raised by Geelen and Kapadia [Combinatorica, 2017] in the context of computing the girth and cogirth of certain types of binary matroids

Ultrafiltration modeling of non-ionic microgels

Membrane ultrafiltration (UF) is a pressure driven process allowing for the separation and enrichment of protein solutions and dispersions of nanosized microgel particles. The permeate flux and the near-membrane concentration-polarization (CP) layer in this process is determined by advective-diffusive dispersion transport and the interplay of applied and osmotic transmembrane pressure contributions. The UF performance is thus strongly dependent on the membrane properties, the hydrodynamic structure of the Brownian particles, their direct and hydrodynamic interactions, and the boundary conditions. We present a macroscopic description of cross-flow UF of non-ionic microgels modeled as solvent-permeable spheres. Our filtration model involves recently derived semi-analytic expressions for the concentration-dependent collective diffusion coefficient and viscosity of permeable particle dispersions [Riest et al., Soft Matter, 2015, 11, 2821]. These expressions have been well tested against computer simulation and experimental results. We analyze the CP layer properties and the permeate flux at different operating conditions and discuss various filtration process efficiency and cost indicators. Our results show that the proper specification of the concentration-dependent transport coefficients is important for reliable filtration process predictions. We also show that the solvent permeability of microgels is an essential ingredient to the UF modeling. The particle permeability lowers the particle concentration at the membrane surface, thus increasing the permeate flux.Comment: 19 pages, 11 figures (Electronic Supplementary Information included: 2 pages, 1 figure

Dynamics of suspensions of hydrodynamically structured particles: Analytic theory and experiment

We present an easy-to-use analytic toolbox for the calculation of short-time transport properties of concentrated suspensions of spherical colloidal particles with internal hydrodynamic structure, and direct interactions described by a hard-core or soft Hertz pair potential. The considered dynamic properties include self-diffusion and sedimentation coefficients, the wavenumber-dependent diffusion function determined in dynamic scattering experiments, and the high-frequency shear viscosity. The toolbox is based on the hydrodynamic radius model (HRM) wherein the internal particle structure is mapped on a hydrodynamic radius parameter for unchanged direct interactions, and on an existing simulation data base for solvent-permeable and spherical annulus particles. Useful scaling relations for the diffusion function and self-diffusion coefficient, known to be valid for hard-core interaction, are shown to apply also for soft pair potentials. We further discuss extensions of the toolbox to long-time transport properties including the low-shear zero-frequency viscosity and the long-time self-diffusion coefficient. The versatility of the toolbox is demonstrated by the analysis of a previous light scattering study of suspensions of non-ionic PNiPAM microgels [Eckert et al., J. Chem. Phys., 2008, 129, 124902] in which a detailed theoretical analysis of the dynamic data was left as an open task. By the comparison with Hertz potential based calculations, we show that the experimental data are consistently and accurately described using the Verlet-Weis corrected Percus-Yevick structure factor as input, and for a solvent penetration length equal to three percent of the excluded volume radius. This small solvent permeability of the microgel particles has a significant dynamic effect at larger concentrations.Comment: 25 pages, 24 figure

A tuning rule based on internal model control and the Nyquist criterion

If the process contains a delay (dead time), the Nyquist criterion is well suited to derive a PI or PID tuning rule because the delay is taken into account without approximation. The tuning of the speed of the closed loop enters naturally by the crossover frequency. The goal of robustness and performance is translated into the phase margin

Paul’s Usage of the Anthropological Term νοῦς

The lexeme νοῦς has received little attention in Pauline exegesis. The few relevant studies on Paul’s use of νοῦς rely solely on Josephus’ use of the term. In order to overcome this one-sidedness, this article understands νοῦς against both a Jewish-Hellenistic and a Graeco-Roman horizon by grasping the range of its meaning in terms of a semantic frame. From there it becomes clear that Paul uses the word in the sense of a psychic faculty and not in the sense of a single thought—a conclusion that is quite different from those of former approaches, which contend that he means both at the same time. These insights will be illustrated by Paul’s use of the lexeme in the opening chapters of 1 Corinthians

Message framing to encourage sustainable fashion consumption : the interaction of materialism and gender

In an era of fashion overconsumption, resources both human and natural are being exploited, and the question is raised on how to confront the abrupt growth of social and environmental problems. As fashion-related issues are geographically too far in distance for the daily consumer to properly register, social marketers need to address topics that are more easily perceivable to initiate change. This dissertation examines the impact of message framing on different consumer attitudes. For this purpose, gender and materialism are acting as moderators in a three-way interaction study. This current study aims to add value to the emerging field of behavioral economics and in particular to loss aversion theory. Furthermore, the author wishes to contribute useful learnings on the topics of gender and materialism studies and, most importantly, create an effective tool for social marketers to promote sustainable fashion consumption. The findings suggest that message framing has no main effects on consumer attitudes unless gender and materialism are being introduced as impactful moderators to the study design. Then, people high in materialism show significant gender differences. High materialistic female participants are more responsive to loss-framed messages, while high materialistic male participants are more sensitive to gain-framed messages. However, the findings also suggest that the two gender types are drawn by different motivations. These outcomes highlight the relevance of message framing combined with gender and materialism studies and show how these techniques can have a real impact when used precisely.Numa era de consumo excessivo na indústria da Moda, tanto recursos humanos como naturais estão a ser explorados, o que levanta a questão de como confrontar o abrupto crescimento dos problemas sociais e ambientais que daí advêm. Uma vez que as questões relacionadas com a Moda estão geograficamente inatingíveis para o consumidor as perceber, é necessário que os responsáveis pelo marketing social abordem tópicos que sejam mais facilmente propensos a iniciar mudança. Esta dissertação examina o impacto do enquadramento de mensagens em diferentes atitudes dos consumidores. Com este objetivo, o género e o materialismo são considerados moderadores num estudo de interação trilateral. Este estudo tem o intuito de acrescentar valor à área emergente da Economia Comportamental, e em particular à teoria de aversão da perda. Adicionalmente, o autor deseja contribuir com conhecimentos úteis para estudos de género e materialismo e sobretudo criar uma ferramenta eficaz para os responsáveis de marketing social promoverem consumo sustentável na Moda. Os resultados sugerem que o enquadramento da mensagem não tem efeitos na atitude do consumidor, a não ser que o género e o materialismo sejam introduzidos como moderadores impactantes na construção do estudo. Deste modo, pessoas com grau elevado de materialismo mostram diferenças significativas em função do género. Participantes do sexo feminino com um grau elevado de materialismo são mais recetivas a uma perda de enquadramento de mensagens, enquanto participantes do sexo masculino são mais sensíveis a um ganho de enquadramento de mensagens. No entanto, os resultados também sugerem que os dois géneros são influenciados por diferentes motivações. Estas conclusões destacam a relevância do enquadramento da mensagem combinado com estudos de género e materialismo, e mostram o modo como estas técnicas podem ter impacto quando usadas de forma precisa